The present invention relates to a polyoxymethylene copolymer which not only exhibits a high crystallization rate, high stiffness and excellent thermal stability but also has excellent secondary shrinkage and gas barrier properties to organic solvent gases, and to a composition thereof.
A polyoxymethylene resin is a polymer material which is widely used for electrical and electronic apparatus parts, automobile parts, and the like since it is easily crystallizable, and molded products thereof are excellent in mechanical properties such as stiffness, thermal resistance and creep resistance. However, oxymethylene units constituting the polyoxymethylene resin are thermally unstable. Therefore, for the purpose of preventing chain by chain depolymerization which starts from unstable terminal groups, the polyoxymethylene resin is usually applied to practice after thermal stability thereof has been generally improved, by copolymerizing a cyclic ether or a cyclic formal having oxyalkylene units capable of introducing carbon-carbon bonds in polymer chains such as ethylene oxide, propylene oxide, 1,3-dioxolane, 1,4-butane diol formal, and further compulsorily removing unstable molecular ends.
Since the oxyalkylene unit decreases the crystallization temperature of the copolymer, the commercial polyoxymethylene copolymer has a melting point of about 160xc2x0 to 165xc2x0 C. while the polyoxymethylene homopolymer without oxyalkylene units has that of higher than 170xc2x0 C. Further, at the cooling step during molding, crystallization does not sufficiently proceed, and the stiffness which is highly dependent on the degree of crystallinity also decreases in general according to the increase of oxyalkylene units. Accordingly, there has been a demand for a polyoxymethylene copolymer which has a low content of the oxyalkylene units, has high thermal resistance and high stiffness, and exhibits sufficient thermal stability even if the content of the oxyalkylene units is decreased.
For the purpose of solving the above problems, as attempts to put into practical use a copolymer having a low content of an oxyalkylene unit and being excellent in stiffness, Japanese Patent Publication Examined No. 6-86509 and Japanese Patent Publication Unexamined No. 5-5017 (corresponding U.S. Pat. No. 5,288,840) propose a technology to make the distribution of polymer chains as uniform as possible and provide the polymer chain terminals, which becomes a starting point of thermal decomposition, with specific substituents. Japanese Patent Publication Unexamined No. 4-145115 proposes to synthesize polymers according to the same viewpoint as the above prior art and make harmless by neutralization components which accelerates decomposition of the polymer chain.
According to these technologies, there surely can be obtained a material which is excellent in tensile strength and resistance to alkali chemicals, is difficult to be thermally decomposed, and exhibits less reduction in strength when left under high temperature circumstances. However, the polyoxymethylene copolymer according to these technologies is produced by having focused on improving the thermal stability in the region where the amount of copolymer comonomer is small, and, as to the improvement of mechanical properties, only the comonomer amount is reduced as a means thereof. Therefore, from the standpoint of improving the stiffness as a mechanical property, there has remained room for improvement.
As for the proposals to enhance the crystallization rate of polyoxymethylene resins having a normal melting point, for example, Japanese Patent Publication Unexamined Nos. 08-59767 and 08-325341 disclose production methods using 1,3-dioxolane as a comonomer and a specific amount of a polymerization initiator. However, even though the range of the comonomer amount and the relatively high range of the amount of the polymerization initiator used disclosed in these prior documents can improve the polymerization yield, which is targeted therein, they are not sufficient to satisfy the demand for the essential improvement in stiffness since the melting point of the copolymer itself is too low.
Moreover, since the polyoxymethylene resin is a crystalline resin, dimensional changes occur due to post shrinkage, i.e., secondary shrinkage, when the resin is left for a long time or is exposed to the atmosphere of high temperatures after being molded. As a result, the polyoxymethylene resin cannot avoid such a drawback that the application thereof to precision parts is limitative. As a method for improving secondary shrinkage thereof, a method of formulating inorganic fillers has been conventionally known. However, the polyoxymethylene resin composition, wherein inorganic fillers are formulated, is not only inferior in mechanical properties, especially elongation and impact resistance, but also has drawbacks such as poor moldability, low strength at weld parts, and therefore it has a drawback that it is unsuitable for the material of precision parts. As other methods, for example, Japanese Patent Publication Unexamined No. 4-108848 proposes to achieve low secondary shrinkage by blending a polyoxymethylene homopolymer and a polyoxymethylene random copolymer at a predetermined ratio. However, this method employs a polyoxymethylene homopolymer which is essentially poor in thermal stability so that the resultant polymer does not exhibit sufficient thermal stability.
On the other hand, the polyoxymethylene resin is a crystalline resin having an extremely high degree of crystallinity. Therefore, it can be said a resin which, in general, is unlikely to permeate an organic solvent gas, has excellent organic solvent gas barrier properties. For instance, a polyoxymethylene resin, which does not permeate butane, propane, and the like, would be an excellent material for use as a pressure vessel, such as a gas lighter. In view of the recent rising demand for energy saving relating to the earth""s environmental problems, lightening of automobile parts with the use of resins, especially fuel related parts of automobile, has been accelerated, and further improvement in the gas barrier property of the resins to automobile fuels such as gasoline and methanol has been required.
The present inventors have found that a polyoxymethylene copolymer having a melting point not lower than 167xc2x0 C. and not higher than 173xc2x0 C., wherein a low-molecular weight polyoxymethylene copolymer which is contained in the polyoxymethylene copolymer and is extractable with chloroform is not more than 5000 ppm, exhibits not only high stiffness and excellent thermal stability but also has excellent secondary shrinkage and organic solvent gas barrier properties. As a result, the present invention has been accomplished.
Namely, the present invention relates to a polyoxymethylene copolymer having a melting point not lower than 167xc2x0 C. and not higher than 173xc2x0 C., wherein a low-molecular weight polyoxymethylene copolymer which is contained in the polyoxymethylene copolymer and is extractable with chloroform is not more than 5000 ppm, and to a polyoxymethylene resin composition containing the polyoxymethylene copolymer, further comprising, based on 100 parts by weight of the polyoxymethylene copolymer,
(A) 0.01 to 5 parts by weight of at least one selected from the group consisting of an antioxidant, a polymer or a compound containing a formaldehyde reactive nitrogen or a catching agent of formic acid, a weathering (light) stabilizer, a mold release agent (a lubricant), and a crystalline nucleating agent,
(B) 0 to 60 parts by weight of at least one selected from the group consisting of a reinforcing material, and an electrically conductive material, a thermoplastic resin, and a thermoplastic elastomer, and
(C) 0 to 5 parts by weight of a pigment.
Further, the present invention provides a molded product obtainable by subjecting the polyoxymethylene copolymer or the composition thereof to injection molding, extrusion molding, blow molding, or pressure molding; a part obtainable by subjecting the polyoxymethylene resin composition to injection molding, extrusion molding, blow molding, or pressure molding, or further subjecting the molded product to processing of cutting after the molding; a working part such as a gear, a cam, a slider, a lever, an arm, a clutch, a joint, an axis, a bearing, a key-stem, a key-top, a shutter, a reel, a part mating and sliding with a leading screw which drives a pick-up for an optical disc drive, a gear which rotates a leading screw, a rack gear which drives a pick-up, and a gear which mates with the rack gear and drives it; a resinous part by outsert molding; a resinous part by insert molding; a chassis; a tray; a side plate; and the like. These parts are particularly used for office automation (OA) apparatuses represented by a printer and a copying machine; for cameras and video apparatuses represented by a video tape recorder (VTR), a video movie, a digital video camera, a camera, and a digital camera; for apparatuses for music, image, or information represented by a cassette player, a laser disc. (LD), a digital audio tape (DAT), a mini disc (MD), a compact disc (CD) [including CD-ROM (read only memory), CD-R (recordable) and CD-RW (rewritable)], a digital video disc (DVD) [including DVD-ROM, DVD-R, DVD-RW, DVD-RAM (random access memory) and DVD-Audio], other optical disc drives, a micro floppy disc (MFD), a magnet optical disc (MO), a navigation system, and a mobile personal computer; for telecommunication apparatuses represented by a cellular phone and a facsimile machine; for interior or exterior parts for an automobile such as fuel related parts represented by a gasoline tank, a fuel pump module, valves, and a gasoline tank flange, door related parts represented by a door lock, a door handle, a window regulator, and a speaker grille, seat belt related parts represented by a slip ring for a seat belt and a press bottom, parts for a combination switch, switches, and clips; and for miscellaneous industrial goods represented by a disposable camera, a toy, a fastener, a chain, a conveyor, a buckle, sporting goods, a vending machine, furniture, an instrument and an apparatus for house-building.
The present inventors made intensive and extensive studies. As a result, they unexpectedly found the fact that low molecular weight components existing in the polyoxymethylene copolymer greatly influence the stiffness, thermal stability, secondary shrinkage, and the organic solvent gas barrier properties, particularly in the compositional region where the amount of the comonomer used is small. Although a specific mechanism of such a phenomenon is not clear, this is supposed to be presumably because the existence of an oligomer affects the crystallization temperature, the crystallization rate or the like so that the degree of crystallinity or the crystal structure is changed.
Although it is not apparent where the oligomer is generated, it is supposed that both of the polymerization process and the decomposition process of unstable parts of the terminal group of the copolymer participate. Particularly, when a specific unstable terminal group is decomposed using a specific amount of a specific cation polymerization catalyst and a specific comonomer, a desirable copolymer containing a smaller amount of oligomer can be obtained.
Specifically, the copolymer of the present invention which is excellent in stiffness, secondary shrinkage, and an organic solvent gas barrier property can be obtained by preferably copolymerizing trioxane and 1,3-dioxolane, and is characterized in that the melting point is not lower than 167xc2x0 C. and not higher than 173xc2x0 C., and the amount of the lower molecular weight polyoxymethylene which is extractable with chloroform is not more than 5000 ppm.
Hereinafter, the present invention is described in detail.
The polyoxymethylene copolymer of the present invention having a melting point of 167xc2x0 to 173xc2x0 C. can be synthesized by reducing the amount of the comonomer to be copolymerized with trioxane against the normal polyoxymethylene copolymer having a melting point of 160xc2x0 to 165xc2x0 C. However, when the synthesis is carried out without special technical attention, a copolymer practically worthwhile cannot be obtained. This is proved by the fact that no product made of a polyoxymethylene copolymer having the melting point falling in this region has existed. The task of the present invention is to improve stiffness of the copolymer without deteriorating thermal stability as compared with conventional technology. The present inventors have made studies to maintain thermal stability of the copolymer by introducing comonomer components in as small an amount as possible. As a result, they succeeded in. improving stiffness itself while maintaining thermal stability, and at the same time in improving secondary shrinkage and the organic solvent gas barrier properties.
In general, when a polyoxymethylene copolymer having high stiffness, that is, having a higher degree of crystallinity, is tried to obtain, it is more preferable as a crystallization starting temperature, i.e., a melting point, is higher. This is probably because the crystallization starts in a high temperature state where a resinous viscosity is still low (in a high fluidity state) at a cooling step of molding, and therefore, the arrangement of molecular chains proceeds more promptly. The polyoxymethylene copolymer of the present invention having excellent stiffness is such a copolymer that has a melting point of not lower than 167xc2x0 C. and not higher than 173xc2x0 C., preferably not lower than 167xc2x0 C. and not higher than 171xc2x0 C. When the melting point is lower than 167xc2x0 C., the stiffness is not sufficiently improved. When it is higher than 173xc2x0 C., it is necessary to add a large amount of a thermal stabilizer and the like for securing practically sufficient thermal stability, so that the melting point thereof is unfavorably substantially lowered.
It has been well known to the public that the melting point of the polyoxymethylene copolymer is determined mainly by the comonomer content, and the melting point therefore mainly controls the crystallization rate and further controls the degree of crystallinity of the resultant molded product, i.e., the stiffness of the product, when the composition is molded. The present inventors have found that the oligomer in the copolymer also influences the crystallization rate. Namely, in the high melting point region where a comonomer content is small, the composition containing a larger amount of oligomer exhibits a decreased crystallization rate so that the degree of crystallinity, accordingly, stiffness, is reduced even if the copolymers have the same comonomer content. The polyoxymethylene resin has not been noticed until today since it is a highly crystallizable polymer material as compared with polyamide resins or polyolefin resins. However, the present inventors have found the fact that the oligomer influences stiffness. Further, they have also unexpectedly found that the oligomer has a great influence on secondary shrinkage and an organic solvent gas barrier property.
The oligomer of the present invention means a component extracted from the powder of the polyoxymethylene resin composition at the side of soluble matters during 24 hour Soxhlet extraction using chloroform. According to a proton NMR and a mass spectrometric analysis, the main component of the oligomer is a compound having a tetramer to a hexadecamer of formaldehyde, which means a compound having a molecular weight of about 120 to 480. In order for the copolymer of the present invention to maintain the excellent stiffness, an allowable oligomer amount is not more than 5000 ppm, preferably not more than 3000 ppm. Ideally, it is required not to contain oligomer at all. However, in the range of the production technology, practical in industry, it is unrealistic, for instance, to make the amount of the polymerization initiator extremely small for maintaining the polymerization rate. Therefore, it cannot be avoided to contain the oligomer in an amount of not less than 100 ppm. In a laboratory, it is possible to conduct a step for extracting and removing the oligomer from products such as a pellet using a solvent for the purpose of reducing it. However, considering the labor hours accompanied by this step, value deterioration as an industrial product cannot be avoided. In other words, the composition which is worth being applied to practical use contains the oligomer in an amount of not less than 100 ppm and not more than 5000 ppm, preferably not less than 100 ppm and not more than 3000 ppm.
When a commercial polyoxymethylene resin material is subjected to the above-described analysis, various additives including an antioxidant are extracted together with the oligomer components. These additives are also thought to be in relation to decrease of the crystallization rate. However, even, for instance, the antioxidant represented by a hindered phenol is added in a usual amount, a large reduction in stiffness is not observed.
The first feature of an industrially producing method of the present invention is a selection of a comonomer to be used for the copolymerization. The comonomer used in the polyoxymethylene copolymer includes ethylene oxide, propylene oxide, 1,3-dioxolane, 1,4-butandiol formal, and the like. Generally, usual polyoxymethylene copolymers having a melting point of 160xc2x0 to 165xc2x0 C. do not exhibit remarkable difference in characteristic properties of the compositions thereof depending upon differences of sorts of the comonomers. In the case of the copolymer of the present invention having a melting point of 167xc2x0 to 173xc2x0 C., 1,3-dioxolane is particularly effective for synthesis of a composition containing less amount of the oligomer. Among 1,3-dioxolane, a 1,3-dioxolane having an acetaldehyde content of preferably not more than 2000 ppm, more preferably not more than 1000 ppm, particularly preferably not more than 200 ppm, is effective. When the acetaldehyde content is over 2000 ppm, it is difficult to prepare a composition with a small amount of the oligomer. The amount of the comonomer used for the polymerization of the copolymer of the present invention is 0.0015 to 0.025 mol, preferably 0.002 to 0.02 mol, more preferably 0.003 to 0.018 mol, based on 1 mol of trioxane.
Secondly, the type and the amount of a cationic polymerization catalyst used for the polymerization are important. In the present invention, it is effective to use, as a polymerization catalyst, at least one selected from the group consisting of boron trifluoride, a hydrate of boron trifluoride, and a complex compound coordinating an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride. Among them, boron trifluoride diethyl ether and boron trifluoride di-n-butylether are preferably exemplified. In general, the amount of the polymerization catalyst used in the synthesis of polyoxymethylene is decided in view of a polymerization rate and a molecular weight of a product. In the present invention, the amount of the oligomer also influences the amount of a catalyst, and there exists a range of the usable amount of the polymerization catalyst suitable for obtaining a copolymer with less amount of the oligomer. Specifically, a preferable range of the polymerization catalyst amount to be used is not less than 3 ppm and not-more than 30 ppm based on the produced weight of the copolymer. The catalyst amount defined herein is not a value obtained from a ratio of the portions of the reactive components prepared upon the polymerization, but a value obtained by analyzing the composition actually produced and converting the result while regarding boron trifluoride having been used as a polymerization catalyst. In the case that the amount of the polymerization catalyst used is either above or less than the suitable range, a copolymer having less oligomer is apt not to be obtained. There may be thought such a possibility that when the amount of the catalyst used is small, formaldehyde, which is not involved in the normal reaction, takes part in the production of an oligomer; on the contrary, when the amount of the catalyst used is large, formaldehyde, which is produced by decopolymerization due to the existence of an excess of catalyst, though it is once contained in a polymer chain, takes part in the production of an oligomer.
Thirdly, the heat treatment of an unstable terminal groups, which is conducted after the polymerization, is important, too. Production of an oligomer is thought to be reduced by carrying out this operation promptly. As a catalyst for this operation, a specified quaternary ammonium compound is preferably used. A preferable quaternary ammonium compound employed in the present invention is represented by the formula (1) below:
[R1R2R3R4N+]nXxe2x88x92nxe2x80x83xe2x80x83(1)
wherein:
each of R1, R2, R3 and R4 independently represents an unsubstituted or substituted C1-C30 alkyl group, a C6-C20 aryl group, an aralkyl group wherein an unsubstituted or substituted C1-C30 alkyl group is substituted with at least one C6-C20 aryl group, or an alkylaryl group wherein a C6-C20 aryl group is substituted with at least one unsubstituted or substituted C1-C30 alkyl group, wherein said unsubstituted or substituted alkyl group being linear, branched or cyclic, and said substituted alkyl group having at least one substituent selected from the group consisting of a halogen atom, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group and an amide group, and wherein at least one hydrogen atom of each of said unsubstituted alkyl group, said aryl group, said aralkyl group and said alkylaryl group being optionally replaced by a halogen atom;
n represents an integer of from 1 to 3; and
X represents a hydroxyl group, or an acid residue of a C1-C20 carboxylic acid, a hydroacid excluding a hydrogen halide, an oxoacid, an inorganic thioacid or a C1-C20 organic thioacid. Among them, each of R1, R2, R3 and R4 in the formula (1) is independently preferably a C1-C5 alkyl group or a C2-C4 hydroxyalkyl group, more preferably at least one of R1, R2, R3 and R4 is a hydroxyethyl group. Specifically, there can be exemplified hydroxide of such as tetramethyl ammonium, tetraethyl ammonium, tetrapropyl ammonium, tetra-n-butyl ammonium, cetyl trimethyl ammonium, tetradecyl trimethyl ammonium, 1,6-hexamethylene bis(trimethylammonium), decamethylene-bis-(trimethylammonium), trimethyl-3-chloro-2-hydroxypropyl ammonium, trimethyl(2-hydroxyethyl)ammonium, triethyl(2-hydroxyethyl)ammonium, tripropyl(2-hydroxyethyl)ammonium, tri-n-butyl(2-hydroxyethyl)ammonium, trimethyl benzyl ammonium, triethyl benzyl ammonium, tripropyl benzyl ammonium, tri-n-butylbenzyl ammonium, trimethyl phenyl ammonium, triethyl phenyl ammonium, trimethyl-2-oxyethyl ammonium, monomethyl trihydroxyethyl ammonium, monoethyltrihydroxyethyl ammonium, octadecyl tri(2-hydroxyethyl) ammonium, and tetrakis(hydroxyethyl)ammonium; hydroacid salt such as hydrochloric acid, bromic acid, and fluoric acid; oxoacid salt such as sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, chloric acid, iodic acid, silicic acid, perchloric acid, chlorous acid, hypochlorous acid, chlorosulfuric acid, amid sulfuric acid, disulfuric acid, and tripolyphosphoric acid; thioacid salt such as thiosulfuric acid; carboxylic acid salt such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, pentanoic acid, caproic acid, caprylic acid, capric acid, benzoic acid, and oxalic acid; and the like. Of these, hyroxide(OHxe2x88x92) and salts of sulfuric acid (HSO4xe2x88x92 and SO42xe2x88x92), carbonic acid (HCO3xe2x88x92 and CO32xe2x88x92), boric acid (B(OH)4xe2x88x92) and carboxylic acid are preferable. Among the carboxylic acids, a formic acid, an acetic acid and a propionic acid are particularly preferable. These quaternary ammonium compounds may be used alone or in combination. Further, in addition to the above quaternary ammonium compounds, amines such as ammonia and triethyl amine, which have been conventionally known as a decomposer for unstable terminal groups, may be used together. An amount of the quaternary ammonium to be added is preferably 0.05 to 50 ppm by weight in terms of the amount of nitrogen derived from the quaternary ammonium compound represented by the formula (2) below, based on the total weight of polyoxymethylene copolymer and the quaternary ammonium:
Pxc3x9714/Qxe2x80x83xe2x80x83(2)
wherein P represents the amount (ppm by weight) of the quaternary ammonium compound, based on the total weight of the polyoxymethylene copolymer and the quaternary ammonium compound, numeral 14 is the atomic weight of nitrogen, and Q represents the molecular weight of the quaternary ammonium compound.
When the addition amount of the quaternary ammonium compound is less than 0.05 ppm by weight, the decomposing rate of unstable terminal groups is decreased. When it is more than 50 ppm by weight, the color of the polyoxymethylene copolymer deteriorates after the unstable terminal groups decompose. A preferable heat treatment is carried out at a resinous temperature of not lower than the melting point of the copolymer and not higher than 260xc2x0 C. using an extruder, a kneader and the like. When the resinous temperature is higher than 260xc2x0 C., there may cause problems in the coloring and the decomposition of the polymer main chain (decrease in a molecular weight). Formaldehyde generated during the decomposition is removed under a reduced pressure. A method for adding the quaternary ammonium compound is not particularly limited. There can be exemplified a method comprising adding the compound in an aqueous solution at the step for inactivating a polymerization catalyst, a method comprising blowing the compound to a copolymer powder, and the like. According to any method, it is acceptable if the compound has been added at the heat treatment step of the copolymer. In the case that the compound is charged into an extruder or that a filler or a pigment is formulated using an extruder or the like, it may be possible to attach the compound to resinous pellets and then conduct the decomposition of the unstable terminal groups at the following formulation step. The decomposition of the unstable terminal groups can be also conducted after a polymerization catalyst contained in a polyoxymethylene copolymer obtained by polymerization is inactivated, and it can be conducted without inactivating the polymerization catalyst. As a method for inactivating the polymerization catalyst, a method wherein the polymerization catalyst is inactivated by neutralization in a basic aqueous solution such as amines, can be exemplified as a representative example. Further, without inactivating the polymerization catalyst, the polyoxymethylene copolymer is heated at a temperature not higher than the melting point of the copolymer in an inert gas atmosphere to reduce the polymerization catalyst concentration by volatilization, and then the decomposition of the unstable terminal groups of the present invention may be carried out.
There is no particular limitation on the molecular weight of the copolymer of the present invention. Generally, the stiffness of a molded product depends on the degree of crystallinity, and the degree of crystallinity changes in accordance with a molecular weight of the copolymer and molding conditions. This is the same in the case of the copolymer of the present invention having a melting point of 167xc2x0 to 173xc2x0 C. The change in the crystallization rate caused by the difference in the molecular weights can be treated by controlling molding conditions. A crystalline nucleating agent may be added for the purpose of increasing not only the crystallization rate but also the degree of crystallinity of the copolymer of the present invention. By adding a crystalline nucleating agent in a small amount, further improvement in stiffness can be achieved.
To the polyoxymethylene copolymer, according to the present invention, publicly known additives, thermal stabilizers or the like may be added so long as the addition is not detrimental to the gist of the present invention. There is concern that the additives may decrease the crystallization rate as well as oligomers. However, even if the stiffness is sacrificed to some extent, such an adjustment of addition may be possible in the case wherein thermal stability is markedly improved or specific physical properties such as a sliding property is enhanced.
By formulating an appropriate additive to the polyoxymethylene copolymer of the present invention according to uses thereof, a polyoxymethylene resin composition excellent both in stiffness and thermal stability applicable to practical use can be obtained. Specifically, there can be exemplified a polyoxymethylene resin composition containing, based on 100 parts by weight of the polyoxymethylene copolymer, (A) 0.01 to 5 parts by weight of at least one selected from the group consisting of an antioxidant, a polymer or a compound containing formaldehyde reactive nitrogen, a catching agent of formic acid, a weathering (light) stabilizer, a mold release agent (a lubricant), and a crystalline nucleating agent, (B) 0 to 60 parts by weight of at least one selected from the group consisting of a reinforcing material, an electrically conductive material, a thermoplastic resin, and a thermoplastic elastomer, and (C) 0 to 5 parts by weight of a pigment.
As Component (A) of the antioxidant, hindered phenol type antioxidants are preferable. Specifically, they include, for example, n-octadecyl-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)-propionate, n-octadecyl-3-(3xe2x80x2-methyl-5xe2x80x2-t-butyl-4xe2x80x2-hydroxyphenyl)-propionate, n-tetradecyl-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], 1,4-butanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], 2,2xe2x80x2-methylenebis-(4-methyl-t-butylphenol), tetrakis[methylene-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)propionate]methane, 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]2,4,8,10-tetraoxaspiro(5,5)undecane, N,Nxe2x80x2-bis-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)propionylhexamethylene diamine, N,Nxe2x80x2-tetramethylene-bis-3-(3xe2x80x2-methyl-5xe2x80x2-t-butyl-4xe2x80x2-hydroxyphenol)propionyldiamine, N,Nxe2x80x2-bis-[3-(3,5-di-t-butyl-4-hydroxyphenol)propionyl]hydrazine, N-salicyloyl-Nxe2x80x2-salicylidene hydrazine, 3-(N-salicyloyl)amino-1,2,4-triazol, N,Nxe2x80x2-bis[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl]oxyamide, and the like; preferably, triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate] and tetrakis[methylene-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)propionate]methane. These antioxidants may be used alone or in combination. Further, the antioxidant is preferably formulated in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the polyoxymethylene copolymer.
Examples of Component (A) of the polymer or the compound containing formaldehyde reactive nitrogen include polyamide resins such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12 and nylon 12, and copolymers thereof such as nylon 6/6-6/6-10 and nylon 6/6-12. Further, there can be exemplified a copolymer comprising acrylamide and a derivative thereof, a copolymer comprising acrylamide, a derivative thereof and other vinyl monomers, and a compound containing a formaldehyde reactive nitrogen atom having an amino substituent. As examples of the copolymer comprising acrylamide, a derivative thereof and other vinyl monomers, poly-xcex2-alanine copolymer obtained by polymerizing acrylamide, a derivative thereof and other vinyl monomers in the presence of metallic alcoholate can be exemplified. Moreover, as examples of the compound containing formaldehyde reactive nitrogen atom having an amino substituent, there can be exemplified triazine derivatives such as guanamine(2,4-diamino-sym-triazine), melamine(2,4,6-triamino-sym-triazine), N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, N,Nxe2x80x2,Nxe2x80x3-triphenylmelamine, N-methylolmelamine, N,Nxe2x80x2,Nxe2x80x3-trimethylolmelamine, benzoguanamine(2,4-diamino-6-phenyl-sym-triazine), acetoguanamine(2,4-diamino-6-methyl-sym-triazine), 2,4-diamino-6-butyl-sym-triazine, 2,4-diamino-6-benzyloxy-sym-triazine, 2,4-diamino-6-butoxy-sym-triazine, 2,4-diamino-6-cyclohexyl-sym-triazine, 2,4-diamino-6-chloro-sym-triazine, 2,4-diamino-6-mercapto-sym-triazine, 2,4-dioxy-6-amino-sym-triazine, 2-oxy-4,6-diamino-sym-triazine, N,N,Nxe2x80x2,Nxe2x80x2-tetracyanoethyl benzoguanamine, succinoguanamine, ethylene dimelamine, triguanamine, melamine cyanurate, ethylene dimelamine cyanurate, triguanamine cyanurate, ammeline, and acetoguanamine. These polymers or compounds containing formaldehyde reactive nitrogen may be used alone or in combination. Among the above polymers or compounds containing formaldehyde reactive nitrogen, a polyamide resin is preferable. The resin is formulated in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the polyoxymethylene resin.
As Component (A) of the catching agents of formic acid, there can be exemplified the above amino-substituted triazine, a co-condensation product of the amino-substituted triazine and formaldehyde, for instance, a polycondensation product of melamine and formaldehyde, and the like. As other catching agents of formic acid, there can be exemplified a hydroxide, an inorganic acid salt, a carboxylic acid salt or an alkoxide of an alkali metal or an alkali earth metal. For instance, they include hydroxide of sodium, potassium, magnesium, calcium and barium, and carbonate, phosphate, silicate, borate and carboxylate of the above metals. As the carboxylic acid, saturated or unsaturated aliphatic carboxylic acids having 10 to 36 carbon atoms are preferable, and these carboxylic acids may be substituted with hydroxyl groups. As the aliphatic carboxylic acids, a capric acid, an undecylic acid, a lauric acid, a tridecylic acid, a myristic acid, a pentadecylic acid, a palmitic acid, a heptadecylic acid, a stearic acid, a nanodecanoic acid, an arachic acid, a behenic acid, a lignoceric acid, a cerotic acid, a heptacosanoic acid, a montanoic acid, a melissic acid, a lacceric acid, an undecylenic acid, an oleic acid, an elaidic acid, a cetoleic acid, an erucic acid, abrassidic acid, asorbic acid, alinoleic acid, alinolenic acid, an arachidonic acid, a propiolic acid, a stearolic acid, a 12-hydroxydodecanoic acid, a 3-hydroxydecanoic acid, a 16-hydroxyhexadecanoic acid, a 10-hydroxyhexadecanoic acid, a 12-hydroxyoctadecanoic acid, a 10-hydroxy-8-octadecanoic acid, a dl-erythro-9,10-dihydroxyoctadecanoic acid, and the like. Among them, a dialiphatic calcium derived from a C12-C22 aliphatic acid is preferable. Specific examples include calcium dimyristate, calcium dipalmitate, calcium diheptadecylate, calcium distearate, calcium(myristate-palmitate), calcium(myristate-stearate), calcium(palmitate-stearate), and the like. And, particularly preferred is calcium dipalmitate, calcium diheptadecylate, and calcium distearate. In the present invention, it is particularly effective to formulate 0.01 to 0.2 parts by weight of at least two selected from the group consisting of the above-described calcium salt of a dialiphatic acid derived from C12-C22 aliphatic acid based on 100 parts by weight of the polyoxymethylene copolymer.
Component (A) of the weathering (light) stabilizers is preferably one or at least two selected from the group consisting of benzotriazole type substances, anilide oxalate type substances and hindered amine type substances.
Examples of the benzotriazole type substances include 2-(2xe2x80x2-hydroxy-5xe2x80x2-methyl-phenyl)benzotriazole, 2-(2xe2x80x2-hydroxy-3,5-di-t-butyl-phenyl)benzotriazole, 2-[2xe2x80x2-hydroxy-3,5-bis(xcex1,xcex1-dimethylbenzyl)phenyl]benzotriazole, 2-(2xe2x80x2-hydroxy-3,5-di-t-amylphenyl)benzotriazole, 2-(2xe2x80x2-hydroxy-3,5-di-isoamyl-phenyl)benzotriazole, 2-[2xe2x80x2-hydroxy-3,5-bis-(xcex1,xcex1-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(2xe2x80x2-hydroxy-4xe2x80x2-octoxyphenyl)benzotriazole, and the like. Examples of the anilide oxalate type substances include 2-ethoxy-2xe2x80x2-ethyloxalic acid bisanilide, 2-ethoxy-5-t-butyl-2xe2x80x2-ethyloxalic acid bisanilide, 2-ethoxy-3xe2x80x2-dodecyloxalic acid bisanilide, and the like. These substances may be used alone or in combination.
Examples of the hindered amine type substances include 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(phenylacetoxy)-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-methoxy-2,2,6,6-tetramethylpiperidine, 4-stearyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, 4-phenoxy-2,2,6,6-tetramethylpiperidine, 4-(ethylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(cyclohexylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-teteramethyl-4-piperidyl)-carbonate, bis(2,2,6,6-tetramethyl-4-piperidyl)-oxalate, bis(2,2,6,6-tetramethyl-4-piperidyl)-malonate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, bis(2,2,6,6-teteramethyl-4-piperidyl)-sebacate, bis(2,2,6,6-teteramethyl-4-piperidyl)-adipate, bis(2,2,6,6-teteramethyl-4-piperidyl)-terephthalate, 1,2-bis(2,2,6,6-teteramethyl-4-piperidyloxy)-ethane, xcex1-xcex1xe2x80x2-bis(2,2,6,6-teteramethyl-4-piperidyloxy)-p-xylene, bis(2,2,6,6-teteramethyl-4-piperidyl)tolylene-2,4-dicarbamate, bis(2,2,6,6-teteramethyl-4-piperidyl)-hexamethylene-1,6-dicarbamate, tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,5-tricarboxylate, tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,4-tricarboxylate, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}butyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]2,2,6,6-tetramethylpiperidine, a condensate of 1,2,3,4-butane tetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol and xcex2,xcex2,xcex2xe2x80x2,xcex2xe2x80x2-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol, and the like. The above hindered amine type substances may be used alone or in combination.
Among the above, preferable weathering agents are 2-[2xe2x80x2-hydroxy-3,5-bis(xcex1,xcex1-dimethylbenzyl)phenyl]benzotriazole, 2-(2xe2x80x2-hydroxy-3,5-di-t-butylphenyl)benzotriazole, 2-(2xe2x80x2-hydroxy-3,5-di-t-amylphenyl]benzotriazole, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, and a condensate of 1,2,3,4-butane tetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol and xcex2,xcex2,xcex2xe2x80x2,xcex2xe2x80x2-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol. These weathering (light) stabilizers are preferably formulated in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the polyoxymethylene copolymer.
As Component (A) of the mold release agent, there can be exemplified an alcohol, an aliphatic acid, and an ester thereof, polyoxyalkylene glycol, an olefin compound having an average polymerization degree of 10 to 5000, a silicone, and the like. Of these, an ester of ethylene glycol and a dialiphatic acid derived from a C12-C22 aliphatic acid is preferable; ethylene glycol distearate, ethylene glycol dipalmitate, and ethylene glycol diheptadecylate are particularly preferable. In the present invention, it is particularly effective to formulate 0.01 to 0.9 part by weight of at least two types selected from the group consisting of the esters of ethylene glycol and a dialiphatic acid derived from C12-C22 aliphatic acids based on 100 parts by weight of the polyoxymethylene copolymer.
As Component (A) of the crystalline nucleating agent, there can be exemplified boron nitride, talc, mica, alumina, a compound of boric acid, and the like. These crystalline nucleating agents are preferably formulated in an amount of 0.01 to 0.1 part by weight based on 100 parts by weight of the polyoxymethylene copolymer.
In the present invention, there may formulate, to the polyoxymethylene copolymer so long as the formulation is not detrimental to the gist of the present invention, Component (B) of the reinforcing agent represented-by an inorganic filler, a glass fiber, glass beads, a carbon fiber and the like; an electrically conductive material represented by an electrically conductive carbon black, metallic powder, a fiber, and the like; a thermoplastic resin represented by a polyolefin resin, an acrylic resin, a styrenic resin, a polycarbonate resin, an uncured epoxy resin, modified products thereof, and the like; a thermoplastic elastomer represented by a polyurethane type elastomer, a polyester type elastomer, a polystyrene type elastomer, a polyamide type elastomer, and the like. These Components (B) are preferably formulated in an amount of 10 to 40 parts by weight based on 100 parts by weight of the polyoxymethylene copolymer.
To the polyoxymethylene resin composition, there can formulate Component (C) of an inorganic pigment represented by zinc sulfide, titanium oxide, barium sulfate, titanium yellow and cobalt blue; and an organic pigment represented by the types of condensed azo, perinone, phthalocyanine and monoazo; and the like.
Component (C) of a pigment of the present invention is used in an amount of 0 to 5 parts by weight, preferably 0.1 to 1 part by weight based on 100 parts by weight of the polyoxymethylene copolymer. When it is more than 5 parts by weight, thermal stability is unfavorably decreased.
The polyoxymethylene copolymer and the composition thereof of the present invention have excellent stiffness and extremely high thermal stability. Further, they can be subjected to a high cyclic molding since a crystallization period thereof is short. Moreover, they are favorably usable for various parts required for dimensional accuracy since they exhibit less secondary shrinkage. Furthermore, since they have excellent gas barrier properties to organic solvent gases, they are suitably applied to such an use that requires a material property of low gas permeable properties to organic solvent gases, for instance, fuel related parts of an automobile.
The polyoxymethylene copolymer and the composition thereof of the present invention which have various merits as above described are superior to the conventional polyoxymethylene resins and are excellent in various physical properties.
The present invention provides not only a polyoxymethylene copolymer having excellent properties and a composition thereof as stated above, but also provides molded products obtainable by subjecting the polyoxymethylene copolymer and the composition thereof to injection molding, extrusion molding, blow molding or pressure molding for utilizing their excellent properties. Further, it provides a part obtainable by subjecting the polyoxymethylene resin composition to injection molding, extrusion molding, blow molding, or pressure molding, or further subjecting the molded product to processing of cutting after the molding; a working part such as a gear, a cam, a slider, a lever, an arm, a clutch, a joint, an axis, a bearing, a key-stem, a key-top, a shutter, a reel, a part mating and sliding with a leading screw which drives a pick-up for an optical disc drive, a gear which rotates a leading screw, a rack gear which drives a pick-up, and a gear which mates with the rack gear and drives it; a resinous part by outsert molding; a resinous part by insert molding; a chassis; a tray; a side plate; and the like.